Contents

Description

Layers in peat were first
noticed by Heinrich
Dau in 1829.[1] A prize
was offered by the Royal Danish
Academy of Sciences and Letters to anyone who could explain
them. Blytt hypothesized that the darker layers were deposited in
drier times; the lighter, in moister times, applying his terms
Atlantic (warm, moist) and Boreal (cool, dry). In
1926 C.A. Weber[2] noticed
the sharp boundary horizons, or grenzhorizont, in German peat, which matched
Blytt’s classification. Sernander defined subboreal and subatlantic
periods, as well as the late glacial periods. Other scientists have
since added other information.

The classification was devised before the development of more
accurate dating methods, such as C-14 dating and oxygen isotope ratio cycles.
Currently geologists working in different regions are studying sea
levels, peat bogs and ice
core samples by a variety of methods, with a view toward
further verifying and refining the Blytt-Sernander sequence. They
find a general correspondence across Eurasia and North America.

The fluctuations of climatic change are more complex than
Blytt-Sernander period can identify. For example, recent peat core samples at Roskilde Fjord
and also Lake Kornerup in Denmark evidenced 40 and 62 distinguishable
layers of pollen,
respectively. However, no universally accepted replacement model
has been proposed.

Problems

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Dating
and calibration

Today the Blytt-Sernander sequence has been substantiated by a
wide variety of scientific dating methods, mainly radiocarbon dates obtained from
peat. Earlier radiocarbon dates were often left uncalibrated; that
is, they were derived by assuming a constant concentration of
atmospheric radiocarbon. In fact the atmospheric radiocarbon
concentration has varied over time and thus radiocarbon dates need
to be calibrated.

Cross-discipline
correlation

The Blytt-Sernander classification has been used as a temporal
framework for the archaeological cultures of Europe and America. Some have
gone so far as to identify stages of technology in north Europe
with specific periods; however, this approach is an
oversimplification not generally accepted. There is no reason, for
example, why the north Europeans should stop using bronze and start using iron abruptly at the lower boundary of the Subatlantic at 600 BCE. In the warm Atlantic
period, Denmark was occupied
by Mesolithic
cultures, rather than Neolithic, as climate would lead you to
believe. Moreover, the technology stages vary widely globally.

The
sequence

The Pleistocene
phases and approximate calibrated dates (see above) are